1. Field of the Invention
The invention relates to water meters and, more particularly, to an improved drive shaft for water meters which prevents damage to meter components in case one or more components are unable to move due to freezing conditions.
2. Description of the Prior Art
Conventional water meters of the positive-displacement type are used to measure the volume (in gallons or other units) of water consumed by a user, Because users are billed on their consumption, such meters must be highly accurate and operate over a wide range of temperatures and environmental conditions.
Such meters generally include an outer casing or housing formed from a non-ferrous metal, such as bronze, having an inlet and an outlet. Within the meter casing is disposed a measuring chamber which may be formed from a plastic or similar material. The measuring chamber defines a precise and predetermined volume. Disposed within the chamber is a so-called nutating disk or oscillating piston which divides the chamber into two or more portions. A drive spindle is attached at right angles to the center of the nutating disk or oscillating piston. As water flows from the meter inlet, through the measuring chamber and through the meter outlet, it causes the nutating disk or oscillating piston to nutate or oscillate within the measuring chamber. This, in turn, causes the free end of the drive spindle to move through a circular path.
This oscillatory motion of the drive spindle is translated into rotational motion of a drive shaft by means of a rigid arm or arms which engage the free end of the drive spindle. Mounted to the other end of the drive shaft is a circular magnet whose surface is disposed immediately adjacent, but not in contact with, an inner portion of the non-ferrous outer casing of the meter.
Mounted atop the meter is a register for displaying water consumption. This register may be a mechanical display of the dial and pointer and/or odometer wheel type. The mechanical components of the register are coupled to the magnet disposed on the end of the drive shaft by means of a second magnet attached to the register drive shaft and disposed adjacent the bottom portion of the register assembly in such a fashion so that when the register is mounted to the top of the meter casing, the two magnets are magnetically coupled together. Such arrangements are shown, for example, in U.S. Pat. No. 3,002,266 and in product literature published by Schlumberger Industries, Inc. for the Neptunes.RTM. T-10 model water meter.
One problem associated with these conventional register driving mechanisms for water meters is that water is always present in the narrow area between the face of the circular magnet connected to the meter drive shaft and the inside surface of the meter casing. If the meter casing is subjected to freezing conditions, it is possible for a layer of frost or ice to form between the circular magnet and the inside of the meter casing. Under these circumstances, the circular magnet and its associated drive shaft will be "frozen" (i.e. unable to move). However, water in the main line leading to and away from the meter, along with water within the meter's measuring chamber, may not be frozen. Under these circumstances, when a user turns on his faucet or otherwise begins to draw water through the meter, the water pressure on the nutating disk or piston will cause it to begin to nutate or oscillate. If sufficient pressure is applied, the end of the drive spindle may simply snap off the rigid arm formed on the end of the drive shaft. Once the water between the circular magnet and the facing portion of the outer casing thaws, the drive shaft will no longer turn the circular magnet, thus causing loss of registration of water flowing through the water meter. This breakdown will probably not be discovered until the next time the water meter is read by the utility, which may occur only several months later. This results in substantial loss of revenue to the water utility, not to mention the need to shut down the user's water service while the broken meter is being taken out of service and repaired.
A conventional water meter drive shaft may also fail under similar conditions by a slightly different mechanism. If the arm on the end of the drive shaft which engages the drive spindle does not break, the drive shaft itself may twist and snap or the connection between the other end of the drive shaft and the circular magnet may be broken. This connection is normally a tight press-fit of the drive shaft into an opening formed in the center of the circular magnet. If too much pressure is applied to this connection the area of the drive shaft which is press fitted into the circular magnet may strip or the magnet itself may break because of the applied forces.
It would therefore be of great benefit if a conventional drive shaft for a water meter could be improved to eliminate the possibility that the arm which engages the drive spindle could be broken and remove the possibility that forces beyond a predetermined level could be applied to the drive shaft and the connection of the drive shaft to the circular magnet, especially when the meter is subjected to freezing conditions.